"On the contrary, The Philosopher says (De Anima iii, 5) that the active intellect is as a light."

Metaphor in Context

On the contrary, The Philosopher says (De Anima iii, 5) that the active intellect is as a light. But light is not the same in the various things enlightened. Therefore the same active intellect is not in various men.
(I, Q79, A5)